Lecture 11: Potential Exam Questions

1: Give two definitions of evolution and explain them.
a) A change in the genetics (gene frequencies) of a population over time. This is commonly referred to as microevolution.
b) A gradual change in living things from one form to another over the course of time. This is commonly referred to as macroevolution.

2: What are the three types of natural selection we discussed in class? Define them.
a) Stabilizing selection-Natural selection for a trait where mean values are favored and extremes are selected against. i.e. human birth weight, giraffe neck length
b) Directional selection-Natural selection where one extreme for a trait is favored. i.e. horse size has increased as the horses environment has transitioned from forest to grassland
c) Disruptive selection-Natural selection where the mean for a trait is selected against while both extremes are favored. This is rarely seen in nature. It can also lead to speciation. i.e. in some cases natural selection has favored finches with either small, or large beaks, as opposed to medium beaks.

3: What maintains genetic diversity? Why not just have one genotype, the best genotype? Why doesn't natural selection eliminate genetic diversity?
Answer: Mutation is the ultimate source of genetic diversity, but occurs at a relatively low rate; migration is the exchange of individuals from discrete populations can give rise to novel gene combinations; sex, because crossing over in meiosis means that sperm and egg cells are essentially random sets of half of an adults genes: mating produces unique combinations of parental genes in each offspring; changing environment means that a trait that is advantageous one year may not be advantageous the next; trade-offs mean that individuals cannot be perfect across traits because they face trade-offs in energy allocation throughout life. i.e. growth versus reproduction.

4: What is meant by the statement "I'd jump in a river to save two brothers, or 8 cousins?"
Answer: Some explanations of altruism in individuals suggest altruistic behavior is more likely to occur between individuals who share a larger number of genes. Two brothers each have half of the same genes as you, eight cousins each have 1/8th the same genetic material as you.

5: At what level of biological organization does natural selection occur?
Answer: Most say natural selection occurs to populations. Some have argued that natural selection occurs at the level of genes (Richard Dawkin's selfish gene), but we didn't really touch on this in lecture.

6: Describe inclusive fitness and give an example.
Answer: Direct fitness is personal reproduction while indirect fitness is the additional reproduction of relatives that is made possible by an individual’s actions. Direct fitness plus indirect fitness equals inclusive fitness. Belding’s ground squirrel is an example of inclusive fitness. They are small rodents that breed in colonies. The male offspring disperse far away from their native home while female offspring stay close to their native area and breed close by. As a result, females in close proximity to one another tend to be related. They help each other by sounding alarm calls when predators are spotted, thus promoting the fitness of their genetic kin.

7: What are the three essential requirements for natural selection?
Answer: First, there must be some variation for some trait. Second, variation must be heritable. Third, there must be a greater or lesser probability of survival and reproduction due to possession of that trait. We also discussed the fact that organisms must produce more offspring than are necessary to replace themselves.

8: Explain tradeoffs and why they’re important.
Answer: Tradeoffs occur because an organism cannot put all of their resources into more than one character trait; ie. All resources into growth and reproduction all at once. Therefore, they have to choose one or the other. An example used in class was the Douglas Fir, which can either have many cones per tree and narrow ring width or wide ring width and few cones per tree. Another example used in class was the guppies in Trinidad. A fish can either be small and colorful or larger and not colorful.

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